This invention relates to water-based dispersions of solid organopolysiloxane resins which are useful in coating applications where aqueous media are preferable over traditional organic solvent based systems. The present invention provides both water-based silicone dispersions as well as methods for producing such compositions.
Silicone resins are often selected for applications requiring premium properties. These organopolysiloxane resins are known to offer outstanding endurance to environmental conditions such as weathering and extreme heat and cold. Silicone resins have found utility in a variety of applications such as pressure sensitive adhesives and release coatings. Furthermore, they have been found to be particularly useful in the paint industry which is continually seeking coating formulations which offer premium properties. Silicone resin solutions have previously been used in the paint coatings industry as vehicles and binders which are a necessary part of quality paint formulations.
Heretofore silicone resins were ordinarily supplied to formulators in solutions, that is to say, the resin consisted of so many parts by weight of silicone solids in some organic solvent such as xylene or toluene. However, recently the use of such organic solvents has been discouraged due to escalating costs for organic materials and increased concern for environmental considerations. Organic solvent based silicone resins often required the use of costly and cumbersome pollution abatement procedures and equipment. Thus there has been a trend in recent years for silicone resin systems which are water-based and therefore not dependent upon organic solvents.
However, such silicone resins which have been found to have particular utility in the art of paints and other coatings have often been immiscible or otherwise incompatible with aqueous coating systems. The present invention provides for the first time silicone resins which can be readily made into water-based dispersion compositions thereby providing the beneficial properties of silicone resins without the cumbersome necessity of unduly large amounts of organic solvents.
As noted above, silicone resins are intended as high performance coating vehicles which can be used in high temperature-resistant coatings and will generally outperform conventional organic resins in similar applications. Those skilled in the art will recognize that there are a number of silicone resins which can be utilized in coating applications. Those silicone resins provided in U.S. Pat. Nos. 4,028,339 and 4,056,492 (both issued to Merrill) are examples of resins which can be made part of the water-based dispersed compositions of the present invention. Both of these patents are hereby incorporated by reference.
Previously known silicone resins in water media have been in the form of emulsions. However, such compositions require the use of specialized equipment, such as colloid mills which do not lend themselves readily to dispersing solid silicone resins. It is common practice also to use solvent solutions of the resin for emulsification, and this might be considered a step backward in the quest to comply with newly evolving environmental regulations covering solvent emissions.
The present invention, on the other hand, utilizes a dispersion process system based upon a combination of suspension aids comprising certain polymeric additives and anionic and/or nonionic compounds. The total requirement for the suspension aids of the present invention is generally in the range of approximately 0.5 to 50 percent based upon the weight of the silicone resin solids.
The term "dispersions" as used herein is intended to mean a stable suspension of particulate solid silicone resin in aqueous media. It does not include emulsions. Emulsions are the subject-matter of applicant's earlier filed copending U.S. Ser. No. 229,247 filed Jan. 28, 1981, now abandoned.
It is therefore a primary object of the present invention to provide water-based dispersions of organopolysiloxane resins which are useful in coating formulations.
It is another object to provide a system for dispersing solid silicone resins comprising a combination of cellulosic-or vinyl addition-polymer having pendent hydroxyl, alkoxyl or neutralized carboxyl groups.
It is another object to provide a process for producing water-based silicone resin dispersions.
These and other objects will become apparent to those skilled in the art upon consideration of the accompanying description and claims.